This application claims the priority of Germany application 196 10 960.4, filed in Germany on Mar. 20, 1996, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a process for open-end spinning in which at least one sliver is opened to single fibers which form a fiber veil, and in which these single fibers are fed to a rotating collecting surface which is driven transversely to their travel direction, and are withdrawn from the collecting surface in the form of a yarn with twist along a yarn formation line before the completion of one single revolution of the collecting surface, whereby the single fibers are never at any point slowed down in the sliver-to-yarn process.
In a process of this type (U.S. Pat. No. 5,222,352), an opening roller, known from rotor spinning, serves to open the sliver to single fibers, and from which the single fibers are transported through a fiber feed channel in an air-stream to a front surface of a rotating disc. In the case of these types of opening rollers, the fibers usually enter the fiber feed channel at a speed which corresponds to approximately half the speed of the opening roller. The single fibers are then accelerated again in the fiber feed channel. The speed of the single fibers when they reach the rotating disc is therefore very high, whereby the actual acceleration of the single fibers is also unknown. The result is that all spinning elements arranged downstream must have an even higher effective speed, which reaches dimensions which are then normally no longer controllable.
An attempt was made in a similar process (German published patent application 40 40 102) to keep the withdrawal speed down by driving the opening roller at a reduced circumferential speed. This appears to be possible in that the opening roller comprises on its periphery, in addition to its combing structure in the form of teeth or needles, suction openings, which suck the sliver deep into the combing structure and, despite a reduced speed, ensure a good combing effect.
However, by means of the suction of the single fibers, they are transported practically at the circumferential speed of the opening roller, so that the single fibers, despite the reduced circumferential speed of the opening roller, have at least the same speed as in the case of standard opening rollers. In this case a fiber feed channel acting as an additional acceleration channel is also arranged downstream of the opening roller.
It is an object of the present invention to improve a process of the type mentioned above to the extent that the single fibers arrive at the collecting surface at a sufficiently low speed to make the yarn withdrawal speed still controllable in its order of magnitude.
This object has been achieved in accordance with the present invention in that the single fibers are subjected to an exactly predetermined, mechanically controlled speed directly after their separation from the sliver.
The present invention is based on the fact that the single fibers, after their separation from the sliver, are not immediately brought up to their high speed by the combing structure of the opening roller, but rather first must be accelerated from the feed speed to the transport speed. The present invention utilizes these circumstances in that the single fibers opened from the sliver are immediately taken up by the collecting surface, which runs at a controlled, sufficiently low speed, before the single fibers reach an excessive speed. To this end, the collecting surface is disposed in sufficiently close proximity to the combing zone, so that the single fibers reach the collecting surface immediately after being combed from the sliver.
The single fibers are advantageously taken up by a suction transport surface directly after they are combed from the sliver. The suction not only serves to transport the single fibers practically slip-free, but also to ensure that the single fibers are removed quickly and efficiently from the opening device, for example from the combing structure of an opening roller, and fed to the transport surface.
In one embodiment, the transport surface can take over the function of the collecting surface at the same time. In another embodiment the single fibers can be transferred from the transport surface to a separate collecting surface. In the former case, the construction is simpler, in the latter case the single fibers are subjected again to a subsequent drafting before they are spun in into the yarn.
In further embodiments, the circumferential direction of the collecting surface is at least approximately perpendicular to the moving direction of the fiber veil occurring thereon. This results in the single fibers obtaining maximum staggering in a transport direction along the transport surface, whereby any eventual drafting errors caused by the opening device are lessened in their effect.
The spun yarn can be withdrawn from the collecting surface in various directions. In one process, the yarn is withdrawn tangentially to the circumferential direction of the collecting surface. Thus a further directional change is avoided. In another process, the yarn is withdrawn transversely to the circumferential direction of the collecting surface. This results in the collecting surface participating in twisting the yarn.
In a further embodiment, the yarn is withdrawn from the collecting surface immediately after the fiber veil has reached the collecting surface. Thus longer transport paths on the collecting surface are avoided, so that, if required, a plurality of opening devices can be arranged at a single collecting surface.
For carrying out the process, the collecting surfaces can have various forms. In one embodiment, the surface of an air-permeable suctioned sieve belt is provided as a collecting surface. In another embodiment, an air-permeable suctioned ring surface on the front side of a rotating disc is provided as a collecting surface. In a further embodiment, an air-permeable, suctioned circumferential surface of a roller-like rotating disc is provided as a collecting surface. It is important in especially preferred embodiments that the circumferential speed of the collecting surface is greater than the speed of the single fibers at the instant they arrive at the collecting surface, but is slower than the withdrawal speed.
A transfer roller can be arranged upstream of the collecting surface, the moving direction of which transfer roller is transverse to the circumferential direction of the collecting surface. This transfer roller takes up the single fibers directly after they have been opened from the sliver and guides them at a controlled, sufficiently low speed to the collecting surface. The collecting surface has at least the same speed or a slightly higher one than the transfer roller.
The collecting surface can be bordered by lateral guiding surfaces for the above purpose. This means that at the generally rather high transport speeds, the single fibers are prevented from leaving the collecting surface laterally. The collecting surface can be provided with a perforation, in the form of slits disposed transversely to the circumferential direction. Thus, there is no area, as seen in the effective width of the collecting surface, which is not suctioned.
In all cases, an air nozzle, in extension of the yarn formation line, can be arranged downstream of the collecting surface. This air nozzle functions as the actual twist device, while the collecting surface, as required or desired, provides only a slight pre-twist of the yarn.
These and further objects, features and advantages of the present invention will become more readily apparent from the following detailed description thereof when taken in conjunction with the accompanying drawings wherein: